The most frustrated and most stymied it is the fact that the United States of America is the one advanced nation on earth in which we do not have sufficient common-sense, gun-safety laws. Even in the face of repeated mass killings.
Armament should be an illegality everywhere, and some sort of international force should patrol a treaty-bound world. Partial armament is one of those absurdities dear to moderate-minded 'reasonable' men. Armament itself is making war. Making a gun, pointing a gun, and firing it are all acts of the same order. It should be illegal to construct anywhere upon earth any mechanism for the specific purpose of killing men. When you see a gun it is reasonable to ask: 'Whom is that intended to kill?'
Honestly this is not going to change unless the people who want to prevent these kinds of mass shootings from taking place feel at least as passionate, at least as mobilized and well-funded as the NRA and the gun manufacturers are because the politics in Congress are such where even members of Congress who know better are fearful if they vote their conscience and support common sense measures like background checks, they're worried they're going to lose.
Invention breeds invention. No sooner is the electric telegraph devised than gutta-percha, the very material it requires, is found. The aeronaut is provided with gun-cotton, the very fuel he wants for his balloon.
I think we can provide common-sense approaches to the issue of illegal guns that are ending up on the streets. We can make sure that criminals don't have guns in their hands. We can make certain that those who are mentally deranged are not getting a hold of handguns. We can trace guns that have been used in crimes to unscrupulous gun dealers that may be selling to straw purchasers and dumping them on the streets.